Additives for temporarily plugging portions of subterranean formations and methods of using the same

ABSTRACT

The present invention relates to additives for forming fluid loss or diverting agents in aqueous treating fluids used in the treatment of subterranean formations. The additives are combined with the aqueous treating fluid to bring about the precipitation of finely divided solids therein having desired size characteristics.

United States. Patent 1 Dill et a1.

[ ADDITIVES FOR TEMPORARILY PLUGGING PORTIONS OF SUBTERRANEAN FORMATIONS AND METHODS OF USING THE SAME [75] Inventors: Walter R. Dill;.Jiten Chatterji; John A. Knox, all of Duncan, Okla.

[73] Assignee: Halliburton Company, Duncan,

Okla.

[22] Filed: June 19, 1972 [21] Appl. No.: 264,117

[52] US. C1.; 166/282, 166/294 [51] Int. Cl E2lb 33/138, E21b 43/27 [58] Field of Search 166/281. 282, 283. 294,

[56] References Cited UNITED STATES PATENTS 2.272.672 2/1942 Kennedy 166/292 X 1 Mar. 19, 1974 Primary Examiner-Stephen J. Novosad Attorney, Agent, or FirmThomas R. Weaver; C. Clark Dougherty, Jr.; John H. Tregoning [57] ABSTRACT The present invention relates to additives for forming fluid loss or diverting agents in aqueous treating fluids used in the treatment of subterranean formations. The additives are combined with the aqueous treating fluid to bring about the precipitation of finely divided solids therein having desired size characteristics.

14 Claims, No Drawings ADDITIVES FOR TEMPORARHLY PLUGGKNG PORTIONS F SUBTERRANEAN FORMATEQNS AND METHODS OF USKNG THE SAME In the matrix treatment of subterranean oil and gas producing formations wherein a treating solution is introduced to the formation it is often advantageous to temporarily but selectively plug portions of the formation with a solid material so that the treating solution is caused to flow to other portions of the formation. For example, in the matrix aeidizing of permeable limestone and sandstone formations, one of the most important factors affecting the success or failure of the acidizing treatment is the proper distribution of the treating acid over the entire producing interval. Due to variations in the permeability of a producing formation, the treating acid entersthe most permeable portion which has the least resistance to flow thereby increasing the permeability of that portion and causing it to accept ever increasing quantities of the treating acid. In order to prevent this uneven distribution of the acid it must be diverted from the most permeable portions of the formation into the less permeable portions thereof. While a variety of diverting agents have been used for this purpose with varying degrees of success, complete removal of the diverting agent from the formation after treatment is often difficult and expensive to achieve.

Further, in many producing wells migration of loose or incompetent formation sands with the produced fluid is experienced. In order to maintain the sands in the formation, special slotted liners, screens, gravel packs and/or sand packs are often utilized in the area of the producing zone to exclude sand. For example, casing is commonly cemented and perforated in the well bore penetrating a producing matrix with a slotted liner positioned within the casing adjacent to the matrix for retaining a sand pack between the casing and liner, which sand pack acts as a screen. In treating such liner completed producing formations whereby a treating fluid is injected into the formation, it is extremely difficult to divert the treating fluid and obtain proper distribution of the treating fluid over the producing interval. While various diverting agents have been utilized in the treating fluids used in such applications they often cannot be provided in a small enough particle size to pass through the slotted liner, screen or sand pack and divert on the producing interval.

By the present invention novel treating fluid additives are provided which form finely divided solids of desired size in aqueous treating fluids. The solids are subsequentlyremoved from a treated formation by dissolution in produced formation fluids, or if required, the solids may be rapidly removed by a subsequent treatment.

The diverting or fluid loss agent forming additives of the present invention are basically comprised of a relatively water insoluble solid material dissolved in a nonaqueous solvent. When the additive is combined with an aqueous treating fluid, the solid material dissolved in the additive is precipitated in the aqueous treating fluid in finely divided form. The term aqueous treating fluid" is used herein to mean any aqueous liquid or solution used in the treatment of subterranean formations including, but not limited to fracturing waters, e.g., fresh water, brines, etc; and aqueous acid solutions, e.g., 2 percent to 35 percent by weight aqueous solutions of hydrochloric acid, hydrofluoric acid, acetic acid, formic acid and mixtures of said acids.

in the preferred form of the invention an organic solid material is utilized in the additive which is soluble in formation fluids. When the aqueous treating fluid containing such organic solid material has been introduced into the formation, the solid material is subsequently removed from the treated formation by dissolution in formation fluids. Examples of organic solid materials which are particularly suitable for use in accordance with the present invention are benzoic acid, salicylic acid, abietic acid, myristic acid and naphthalene. These organic solid materials have relatively high melting points (above 120F) and limited solubility in aqueous fluids so that they readily precipitate in aqueous treating fluids and function efficiently as diverting agents. Further, the organic solid materials are soluble in produced hydrocarbons to the degree required for removal by dissolution therein. However, if rapid removal of the solid material from a treated formation is required this may be accomplished by flushing the formation with a solvent for the solid material. Of the organic solid materials listed above, benzoic acid, salicylic acid and naphthalene are preferred with benzoic acid being the most preferred.

A variety of non-aqueous solvents can be utilized in accordance with the present invention, e.g., low molecular weight paraffin alcohols such as methanol, propanol and isopropanol; acetone, methyl ethyl ketone; 2- ethoxyethanol; methylformacel; chloroform; and ether. Low molecular weight paraffin alcohols are preferred in that they readily dissolve a variety of solid materials suitable-for use in accordance with the present invention. Of these, isopropanol and methanol are most preferred.

In preparing the additives of the present invention the organic solid material utilized is combined with and dissolved in the non-aqueous solvent used. The particular quantity of solid material dissolved in the solvent depends upon the minimum temperature to which the additive will be exposed. That is, the quantity of solid material dissolved in the solvent should be such that the solid material does not precipitate at the minimum temperature to which the additive will be exposed. For example, an additive of the present invention comprised of benzoic acid dissolved in isopropyl alcohol in the amount of 1 pound of solid benzoic acid per 1 gallon of alcohol precipitates solid benzoic acid at a temperature of 30F. An additive including 2 pounds of benzoic acid per 1 gallon of alcohol precipitates benzoic acid at a temperature of 35F, and an additive having 3 pounds of benzoic acid per 1 gallon of alcohol dissolved therein precipitates benzoic acid at a temperature of F. When methanol is used as the solvent instead of isopropanol and benzoic acid is dissolved therein in a quantity of 1 pound of benzoic acid per 1 gallon of methanol, solid benzoic acid is precipitated at -40F. At 2 pounds of benzoic acid per 1 gallon of methanol precipitation occurs at l2F, and at 3 pounds of benzoic acid per l gallon of methanol, precipitation occurs at 34F.

isopropanol is preferred for use as the solvent in the additives of the present invention in that its handling properties are good. The preferred organic solid material, benzoic acid, is relatively insoluble in aqueous treating solutions and is readily soluble in isopropanol and produced oil and gas. The preferred additive of the present invention is comprised of benzoic acid dissolved in isopropyl alcohol in an amount of about 2 pounds of benzoic acid per 1 gallon of alcohol.

As stated previously, when a diverting agent forming additive of the present invention containing a dissolved organic solid material is combined with an aqueous treating fluid such as an aqueous acid solution, water, brine, etc., the organic solid material is precipitated in the aqueous treating fluid. However, the additive must be added to the aqueous treating fluid in an amount such that a greater quantity of organic solid material is precipitated than that which is subsequently dissolved by the aqueous treating fluid at the highest temperature to which the treating fluid will be exposed. For example, for a percent by weight aqueous hydrochloric acid solution, the solubility of benzoic acid at l50F is 0.046 pounds per gallon. Thus, for a formation treating temperature of 150F, and additive of the present invention containing benzoic acid must be added thereto in an amount greater than that required to precipitate 0.046 pounds of benzoic acid per gallon of HCl solution. The particular quantity of additive and resulting precipitate which should be used over and above that which is dissolved by the aqueous treating fluid depends on a variety of factors such as the particular treatment and permeability of the formation to be treated and the amount of diversion or plugging re quired. Generally, however, a quantity of precipitated solid material in the aqueous treating fluid in the range of from about 10 to about 150 pounds per 1,000 gallons of treating fluid is required.

The size of the particles of solid material precipitated in an aqueous treating fluid upon mixing an additive of the present invention therewith can be controlled by the addition of a surface active agent to the treating fluid, or alternatively, the surface active agent can be included as a component in the additive. The presence of a surface active agent in the treating fluid also brings about the proper dispersion of the precipitated solid particles therein.

A great variety of commercially available surface active agents may be utilized in accordance with the present invention. The surface active agents may be anionic, cationic, nonionic, amphoteric, or blends thereof. The criteria for selecting a particular surface active agent for use in accordance with the present invention are as follows:

l. The surface active agent controls the particle size of the precipitated solid material which results when an additive of the present invention is added to a particular aqueous treating fluid. Thus the particular surface active agent used must bring about the precipitation of solid material in the particle size required for the particular job to be accomplished with the treating fluid.

2. The surface active agent should effectively disperse the solid precipitate throughout the treating fluid.

3. The surface active agent should be compatible with the particular formation to be treated.

When the preferred additive of the present invention, i.e., benzoic acid dissolved in methanol or isopropanol, is utilized in an aqueous acid solution, fluffy particles of benzoic acid are precipitated if the acid solution or additive does not contain a surface active agent. When a commercially available surface active agent such as acetyl trimethyl ammonium chloride, benzyl trimethyl ammoniumchloride, a betaine, or an alkylsulfonate is present in the aqueous acid solution, either by direct addition to the acid solution or by addition thereto as a component of the amount in an mount in the range of from about 0.2 percent to about 1.0 percent by weight of acid solution, large granular particles of solid benzoic acid (larger than about microns) result. If highly dispered benzoic acid particles fine enough to pass through a 20-40 mesh sand pack (less than about 100 microns) are required, surface active agents such as a nonionic ethoxylated straight chain alcohol, a nonionic blend of an ethoxylated sodium salt of an amphoteric compound and acetyl phenoxy polyethoxy phenol, or a blend of a nonionic surfactant and an anionic amphoteric surfactant can be used in the acid solution in an amount in the range of from about 0.2 percent to about 0.5 percent by weight to bring about this result. When very finely divided benzoic acid particles are required, i.e., particles which will pass through a 20-40 mesh or a 40-60 mesh sand screen and divert on formation sand, surface active agents such as a nonionic ethoxylated straight chain alcohol or an ethoxylated sodium salt of an amphoteric compound and acetyl phenoxy polyethoxy phenol can be utilized in the treating solution in an amount of from about 0.5 percent to about 1.0 percent by weight of treating solution.

The preferred surface active agent for use with the preferred benzoic acid additive of the present invention is a commercially available nonionic ethoxylated straight chain alcohol. When the surface active agent is utilized as a component part of the additive, its concentration therein can vary from 0.2 percent to 3 percent by weight depending upon the type and quantity of precipitated solids which are desired in the aqueous treating solution.

in an alternate aspect of the present invention an additive for bringing about the precipitation of a solid organic acid in an aqueous acidizing treating solution is provided. A water soluble salt of benzoic acid or salicylic acid is dissolved in water and the resulting aqueous additive is combined with an aqueous acid treating solution to be utilized in acidizing a subterranean formation. When the aqueous salt solution additive mixes with the acid treating solution, solid organic acid is precipitated in the same manner as described above and the size and dispering properties of the particles can be controlled through the addition of a surface active agent to the additive or the acid solution as described above. A preferred additive of this type is one prepared by dissolving ammonium benzoate. in water in an amount in the range of from about 0.075 pounds to about 1.8 pounds per 1 gallon of water.

in order to insure a clear understanding of the present invention, the following examples are given:

EXAMPLE 1 An additive of the present invention is prepared by dissolving benzoic acid in methanol in an amount of 2.7 pounds of benzoic acid per 1 gallon of methanol. Portions of the additive are combined with 15 percent by weight aqueous hydrochloric acid solutions in amounts of 3 percent by volume of acid. The acid solutions contain various concentrations of various surface active agents as noted in Table I below. The resulting acid solutions containing solid benzoic acid precipitate are observed for precipitate appearance, dispersion of the precipitate in the acid solutions and how long the precipitate remains suspended in the solutions. The results hydrochloric acid Solutions Percent y Weight of these tests are shown in Table I below.

TABLE 1.- aoPeRrras OF PEECIIJITATE roiiiiie iiripgag USING VARIOUS SURFACE ACTIVE AGENTS TN THE HCl SOLUTIONS Concentration of surface I active agent in HCl Time precipitate remains solution, percent by Appearance of benzoic acid Dispersing properties of suspended in solution,

Surface active agent used volume of acid solution precipitate precipitate minutes*** Fluffy Good .2 Coarse-granular.. Good... 5 .4 Coarse-granular.. Good... 5 .6 Fine-granular Good... 10 .8 Fine-granular... Good... 10 .0 Fine-granular Good... 7 .l Coarse-granular.. Good... 3 .2 Fine-granular..... Good... .3 Fine-granular... Good... .4 Fine-granular... Good... 25 .5 Fine-granular Good *Acommercially available blend of a nonionic surfactant and an anionic amphoteric surfactant.

A commercially available nonionic ethoxylated straight chain alcohol. ***Settling of solids detected at times listed. When fine-granular particles resulted, settling occurred slowly.

I 25 effectiveness of the diverting agent forming additives and methods of the present invention. A 2-inch internal diameter column containing a 3-inch lower layer of 70-170 mesh (U.S. Sieve Series) sand and a 2-inch 30 upper layer of 20 40 mesh sand is used. The 70-170 v V mesh sand has a permeability of 9 darcies and simulates EXAMPLE 2 the producing formation. The 20-40 mesh sand has a permeability of 121 darcies and simulates a sand pack or screen. A variety of acid treating solutions are prepared by combining a methyl alcohol-benzoic acid additive of the present invention (2.7 pounds of benzoic acid per l gallon of solution) with 15 percent aqueous hydrochloric acid solutions in various amounts. Vari- From the foregoing, it can be seen that the particle size of the precipitate formed can be controlled through the use of a particular quantity of selected surface active agent in the treating solution.

Various quantities of various surface active agents are added to portions of the methanol-benzoic acid additive described in Example 1 above. The resulting methanol-benzoic acid-surfactant mixtures are combined with 15 percent by weight aqueous hydrochlori id ous surface active agents are added to the 15 percent l ti i an amount f 3 rc t b vol me (ba d aqueous hydrochloric acid solutions in various amounts on the volume of acid solution) with stirring. The reprior to combining the additives therewith. The treatsulting precipitates are observed for appearance, dising solutions containing precipitated diverting agent persion properties and time in suspension. The results are each flowed downwardly through the column at a of these tests are shown in Table II below. constant differential pressure of 40 psi and a tempera- TABLE II.PROPERTIES OF PRECIPITATE FORMED IN 15%iI-ICI SOLUTIONS USING VARIOUS SURFACE ACTIVE AGENTS IN THE PRECIPITATE FORMING ADDITIVES Concentration of surface active agent in methanol-benzoic acid Time precipitate remains additive, percent by Appearance of benzoic acid Dispersing properties of suspended in solution, Surface active agent used volume of additive precipitate precipitate 1 minutes 1.0 Fluffy.. Good 30+ 2.0 Fluffy Good 30+ 3.0 Granular-fine.. Good 10 0.1 Fluffy Good. 30+ 0.2 Fluffy Good. 30v 0.3 Fluff Good..... 30+ 0.4 Granular-fine. Good..... 10 0.5 Granular-fine Good 30 "A Commercially available blend of a nonionic surfactant and an anionic amphoteric surfactant. *A commercially available nonionic ethoxylated straight chain alcohol.

ture of 76F. The diverting ability of the precipitate formed in the acid treating solutions is determined by w. noting the decrease in flow through the column and de- Laboratory tests simulating the injection of aqueous crease in permeability thereof during the first 5 min- IEEAMWFLE 3 into sand formations are conducted to determine the utes of e ach testfThe results of these tests are shown which various benzoic acid precipitates are deposited. in Table III. Various surface active agents are added to 15 percent TABLE [ID-PERMEABILITV DECREASE OF SAND wI-IEN FLOWING HC] SOLUTIONS THERETHROUGH CONTAINING DIVERTING AGENT FORMING ADDITIVES Concentration of Surface active agents Percent permeability additive mixed with in acid solution- Flow of HCl solution through column decrease*"** HCl solution, concentration, percent percent by volume by volume of acid First Second Third Fourth Fifth First Second of acid solution v solution minute minute minute minute minute minute minute 2.0 Hajj; 342 82 67 62 60 87 97 3.0 -%Zj. 190 38 30 2s 23 93 98.5

*A commercially available blend of a nonionic surfactant and an anionic amphoteric surfactant.

A commercially available blend of an alkyl benzyl ammonium chloride compound, nonionic ester compounds and nonionic ethoxylate compounds which exhibit the overall characteristics of an anionic surface active agent.

***A commercially available foam inhibitor material.

****Most of the percipitate deposited on the simulated formation sand in each test, i.e., at the interface between the 70-170 mesh sand and the -40 mesh sand.

The operability of the additives and methods of the 'fiyiikightaq'uisus hydrochloric acid solutions in an present invention at a differential pressure of psi is amount of 0.5 percent by volume of the 'acid solution. illustrated by the above data. An additive of the present invention (2.7 pounds of 35 benzoic acid per 1 gallon of solution) is combined with EXAMPLE 4 each test acid solution in an amount of 3 percent by Tests similar to those described in Example 3 are volume of solution and the resulting mixture flowed conductedexcept that a cell having a 2 1 inch internal. through the sand tested. The results of these tests are diameter is used and the test acid treating solutions are shown in Table V below.

flowed through the cell at a constant 1,000 psi differen- 4O tial pressure and a temperature of 76F. No surface acc.-..a..-.... tive agent is utilized. The results of these tests are TABLE V.-DEPOSITION OF PRECIPITATE ON VARIOUS SIZES OF SAND USING VARIOUS SURFACE ACTIVE shwn m Table AGENTS IN AcIo SOLUTION MWW Maw M I m I I U H i 7 Size ofsand U.S. s'eve se e TABLE lV.-PERMEABILITY DECREASE OF SAND WHEN Surfa l n s) FLOWING 15% HCl SOLUTIONS THERETHROUGH active 10'-20 EO STQISNING DIVERTING AGENT F R I agent mesh 20-40 mesh 40-60 mesh' 70-170 mesh 1" Passed Passed Deposited..... Deposited. Concentration of Time re- 2* Passed. Passed Passed Deposited. addItIveIn l-lCl Volume of gulred for H 3*"*..... Passed. Deposited..... Deposited...... Deposited. solution, percent acid flowed acId to flow PermeabIlIty 4**** Pa d Deposited Deposited Deposited, by volume of through cell, through cell, decrease, acid solution ml. 566. Per ent *A commercially available blend of a nonionic surfactant and 2300 l 2 O an anlipnic amphotsltl'ic surtzlicltjilint.

- commerci avai a mic ethox lat d t ht h alcohol. y e nonI y e s raig c am I ***A commercially available blend of a nonionic surfactant and 2300 21.0 94 a quaternary ammonium chloride compound. 2300 30-0 96 A commercially available blend of nonionic and anionic 2300 40.0 97 surface active agents.

NOTE: Most of the precipitate deposited on the simulated formatione sand in each test, i.e., at the interface between the 70-l70 .a- .w. M. mum. mesh sand and the 20-40 mesh sand The data presented in Table V illustrates that the par- WWW ticle size of the precipitate formed by the additives Of The operability of the present invention to divert acid the present invention can be selectively controlled. solutions at a differential pressure of 1,000 psi is illus- EXAMPLE 6 trated by the foregoing.

g Y Laboratory tests simulating the injection of aqueous EXAMPLE 5 hydrochloric acid solutions l 5 percent by weight l-ICl) Tests similar to those described in Example 3 are into sand formations are conducted to determine the conducted to determine the size of sand particles on effectiveness of various diverting agent forming additives of the present invention. A 2-inch internal diame- While preferred embodiments of the present inventer column containing a 3-inch lower layer of 70-170 tion have been described for purposes of disclosure, it mesh sand (simulating a 9 darcy permeability producis to be understood that the description and foregoing examples are given to illustrate and explain the invention, and suitable variations may be made within the scope of the appended claims without departing from ing formation) and an upper layer of 20-40 mesh sand (simulating a 121 darcy permeability sand pack) is used. Various additives of the present invention are prepared by dissolving the organic solid materials theinventionnoted in Table VI below in isopropyl alcohol in the What is Claimed I53 quantities given in Table VI. The various additives are A method of p y Plugging Portions of a then combined with aqueous acid solutions(l5 percent Subterranean formation when introducing an by weight HCI containing 0.6 percent by volume of the aqueous treating fluid therein which Comprises the surface active agent noted in Table VI) in an amount steps f of? percent by volume of acid combining an additive with said aqueous treating I fluid which causes the precipitation of a finely di- The resulting acid solutions containing precipitated id d lid r i it te therein;

diverting agent are flowed downwardly through the colintroducing the aqueous treating fluid containing the umn at a constant pressure of 40 psi and a temperature solid precipitate into the formation so that portions of 76F. The diverting ability of the precipitate formed of the formation are plugged by the solid precipiin each of the acid solutions is determined by noting the tate; and

decrease in flow through the column and decrease in subsequently removing the solid precipitate from said permeability thereof during the first five minutes of formation wherein said additive is comprised of a each test. The results of these tests are shown in Table relatively water insoluble organic solid material VI below: dissolved in a non-aqueous solvent.

TABLE VI.-IERMEABILITY DECREASE OF SAND WHEN FLOWING l5% HCl SOLUTIONS THERETHROUGH CONTAIN- ING VARIOUS DIVERTING AGENT FORMING ADDITIVES Percent permeability Concentration of Flow of HCl solution through column, mls. decrease organic solid ma Organic solid material terial, pounds per First Second Third Fourth Fifth First Second in additive gallon of additive minute minute minute minute minute minute minute 2666 Benzoic Acid 2 i065 457 I55 75 32 6O 83 saiieync acid. 2 1190 610 138 I01 76 55 77 Naphthalene... M 0.6 650 340 250 180 150 76 87 Myristic acid.. 2 234 50 25 23 9l 98 Abietic acid 2 335 31 19 9 7 87 99 Acid solutions contain 0.6% by volume of a commercially available blend of a nonionic surfactant and an anionic amphoteric surfactant. Most of the precipitate deposited on the simulated formation sand in each test, i.e., at the interface between the 70-[70 mesh sand and the 20-40 mesh sand.

*"* Isopropanol will dissolve 0.6 pounds of naphthalene per gallon of solution at 76F. 50% by volume of additive combined with acid solution.

EXAMPLE 7 2. The method of claim ll wherein the step of removing the solid precipitate from said formation comprises MCthaH I- fmZ iC addit s C ta n g P unds f producing formation fluids from said formation so that benzoic acid per gallon of solution and various quantithe solid precipitate is dissolved thereby. ties of various surface active agents as noted in Table 3. The method of claim 1 wherein the solvent is a low -VII below are combined with aqueous acid solutions molecular weight paraffin alcohol.

( Percent y Weight in the m unt of 3 percent 4. The method of claim 3 wherein the relatively water by volume of acid. The resulting acid solutions containinsoluble organic solid material is selected from the ing precipitated benzoic acid are observed for precipigroup consisting of benzoic acid, salicylic acid, abietic tate appearance, dispersion of the precipitate in the acid, myristic acid and naphthalene. acid solutions and how long the precipitate remains 5. The method of claim 4 wherein the relatively water suspended in the solutions. The results of these tests are insoluble organic solid material is benzoic acid and the shown in Table VII below: non-aqueous solvent is isopropyl alcohol.

TABLE VII-PROPERTIES OF PRECIPITATE FORMED IN 15% I-ICl SOLUTIONS USING VARIOUS QUANTITIES OF SUR- FACE ACTIVE AGENTIN THE ADDITIVES Concentration of surface active agent in Time precipitate Surface active additive, percent by Appearance of benzoic acid Dispersing properties of remains suspended in agent used weight precipitate precipitate solution, minutes 1.0 Fluffy Good 30+ 2.0 Fluffy Good... 30+

3.0 Granular-fine. Good... I0

0.l Fluffy Good... 30+

0.2 Fluffy..... Good... 30+

0.3 Fluff Good... 30+

0.4 Granular-fine. Good... 10

0.5 Granular-fine Good 30 A commercially available blend of a nonionic surfactant and an anionic amphoteric surfactant. A commercially available nonionic ethoxylated straight chain alcohol.

ll 1 6. The method of claim 1 wherein the additive is further characterized to include a surface active agent mixed therewith.

7. The method of claim 6 wherein the organic solid material is benzoic acid, the non-aqueous solvent is isosubterranean formation when introducing an aqueous acid solution therein which comprises the steps of:

combining with said aqueous acid solution an additive comprised of an aqueous solution of a water 12 soluble salt of a solid organic acid so that the solid organic acid is precipitated in said acid solution in finely divided form;

introducing the aqueous acid solution containing the solid organic acid precipitate into the formation so that portions of the formation are plugged by said precipitate; and

subsequently removing the solid precipitate from the formation.

12. The method of claim 11 wherein the water soluble solid organic acid salt is ammonium benzoate.

13. The method of claim 12 wherein the step of removing the solid precipitate from the formation comprises producing hydrocarbons from the formation so that the benzoic acid precipitate is dissolved therein.

14. The method of claim 13 wherein the step of removing the solid precipitate from the formation comprises flushing the formation with a low molecular weight paraffin alcohol solution so that the precipitate is dissolved therein. 

2. The method of claim 1 wherein the step of removing the solid precipitate from said formation comprises producing formation fluids from said formation so that the solid precipitate is dissolved thereby.
 3. The method of claim 1 wherein the solvent is a low molecular weight paraffin alcohol.
 4. The method of claim 3 wherein the relatively water insoluble organic solid material is selected from the group consisting of benzoic acid, salicylic acid, abietic acid, myristic acid and naphthalene.
 5. The method of claim 4 wherein the relatively water insoluble organic solid material is benzoic acid and the non-aqueous solvent is isopropyl alcohol.
 6. The method of claim 1 wherein the additive is further characterized to include a surface active agent mixed therewith.
 7. The method of claim 6 wherein the organic solid material is benzoic acid, the non-aqueous solvent is isopropyl alcohol and the surface active agent is a nonionic ethoxylated straight chain alcohol.
 8. The method of claim 1 which is further characterized to include the step of adding a surface active agent to the aqueous treating solution prior to combining said additive therewith.
 9. The method of claim 8 wherein the additive is comprised of benzoic acid dissolved in isopropyl alcohol.
 10. The method of claim 9 wherein the surface active agent is a nonionic ethoxylated straight chain alcohol.
 11. A method of temporarily plugging portions of a subterranean formation when introducing an aqueous acid solution therein which comprises the steps of: combining with said aqueous acid solution an additive comprised of an aqueous solution of a water soluble salt of a solid organic acid so that the solid organic acid is precipitated in said acid solution in finely divided form; introducing the aqueous acid solution containing the solid organic acid precipitate into the formation so that portions of the formation are plugged by said precipitate; and subsequently removing the solid precipitate from the formation.
 12. The method of claim 11 wherein the water soluble solid organic acid salt is ammonium benzoate.
 13. The method of claim 12 wherein the step of removing the solid precipitate from the formation comprises producing hydrocarbons from the formation so that the benzoic acid precipitate is dissolved therein.
 14. The method of claim 13 wherein the step of removing the solid precipitate from the formation comprises flushing the formation with a low molecular weight paraffin alcohol solution so that the precipitate is dissolved therein. 